Lithia alumina silica (LAS) materials may be used for applications in which a very low coefficient of thermal expansion (CTE) is desired. Applications include, but are not limited to, thermal shock-resistant structures, nanolithography platforms, and optical windows. One material sometimes used in such applications is beta-eucryptite. However, a problem that may occur while manufacturing beta-eucryptite is the formation of microcracks that reduce the material's strength. Microcracks may also propagate when the material is exposed to additional post-manufacture mechanical or thermal stress. Microcracks are caused by large differences in the CTE between different crystallographic directions (e.g., the c-axis CTE is about −17.6×10−6/° C. while the a- and b-axis CTE is about +8.21×10−6/° C.). These large differences in axial CTE values are referred to in the art as axial mismatch.
Candidate materials for low/zero CTE applications include, but are not limited to, fused silica and eucryptite/oxide composites. However, fused silica is very expensive to make as large bodies and eucryptite/oxide composites exhibit microcracking.
Because of their low or negative CTE, these silica and eucryptite materials are predominantly used to tailor materials with great resistance to thermal shock and good dimensional stability. Traditionally, such materials have been made by combining the negative CTE materials with those having a positive CTE, in order to produce a composite with a desirable CTE. An alternative method involves changing the composition of the material (e.g. by doping) to produce single phase materials with coefficients of thermal expansion that are close to zero. This type of doping method to produce low CTE materials has not been explored with regard to beta-eucryptite materials.
Sol-gel is a process method for producing high purity ceramics and composites.
The present invention overcomes the above mentioned problems by providing doped low thermal expansion materials, including zinc doped beta-eucryptite materials, and methods for making these materials.